Shift register

ABSTRACT

Discussed herein is a shift register which is capable of stabilizing an output thereof. The shift register includes a plurality of stages for sequentially outputting scan pulses in such a manner that high durations of the scan pulses partially overlap with each other. Each of the stages includes a node controller for controlling a charging duration of a set node, and an output unit for outputting a corresponding one of the scan pulses through an output terminal for the charging duration of the set node.

This application claims the benefit of Korean Patent Application No.10-2011-0037394 filed on Apr. 21, 2011 which is hereby incorporated byreference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shift register, and moreparticularly, to a shift register which is capable of stabilizing anoutput thereof.

2. Discussion of the Related Art

In general, a conventional shift register generates scan pulses using aplurality of clock pulses having phase differences therebetween,externally supplied thereto.

Such a clock pulse is periodically input to the drain electrode of apull-up switching device which is in charge of output of the shiftregister. Whenever the clock pulse of a high state is supplied to thedrain electrode of the pull-up switching device, a voltage at a set nodemay gradually increase due to a coupling phenomenon. As a result, thepull-up switching device may be turned on in an undesired period,resulting in unstable output.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a shift register thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a shift register whichis capable of generating a scan pulse using a direct current voltage toremove a coupling phenomenon, so as to stabilize an output thereof.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, ashift register includes a plurality of stages for sequentiallyoutputting scan pulses in such a manner that high durations of the scanpulses partially overlap with each other, wherein each of the stagesincludes a node controller for controlling a charging duration of a setnode, and an output unit for outputting a corresponding one of the scanpulses through an output terminal for the charging duration of the setnode.

The node controller may maintain the charging duration for a timecorresponding to a low duration of any one of a plurality of clockpulses having phase differences therebetween, and the output unit mayoutput the corresponding scan pulse of a high state for the chargingduration by selectively outputting a first charging voltage for thecharging duration, the first charging voltage being a direct current(DC) voltage, wherein the plurality of clock pulses may be sequentiallyoutput in such a manner that low durations thereof partially overlapwith each other.

The output unit may include a pull-up switching device controlled by avoltage at the set node and connected between a first charging voltageline transferring the first charging voltage and the output terminal.

The output unit may further include a pull-down switching devicecontrolled by any one of the clock pulses and connected between theoutput terminal and a first discharging voltage line transferring afirst discharging voltage.

In accordance with one aspect of the present invention, the nodecontroller of an nth one of the stages (where n is a natural number) mayinclude a first switching device controlled by any one of the clockpulses and connected between the output terminal of an (n−p)th one ofthe stages (where p is a natural number less than n) and a preset node,a second switching device controlled by any one of the clock pulses andconnected between the set node and a second discharging voltage linetransferring a second discharging voltage, and a third switching devicecontrolled by a voltage at the preset node and connected between asecond charging voltage line transferring a second charging voltage andthe set node, wherein the first switching device, the second switchingdevice and the pull-down switching device may all be supplied with thesame clock pulse, wherein the clock pulse supplied to the firstswitching device, second switching device and pull-down switching devicemay have a low duration coinciding with a high duration of a scan pulseoutput from the nth stage, wherein the clock pulse supplied to the firstswitching device, second switching device and pull-down switching devicemay have a high duration partially overlapping with a high duration of ascan pulse from the (n−p)th stage.

The clock pulse may have a low voltage lower than or equal to the seconddischarging voltage, the second discharging voltage may be lower than orequal to the first discharging voltage, the clock pulse may have a highvoltage lower than or equal to the first charging voltage, and the firstcharging voltage may be lower than or equal to the second chargingvoltage.

Each of the stages may further include a first capacitor connectedbetween the set node and the output terminal, and a second capacitorconnected between the preset node and the set node.

The node controller of the nth stage may further include a fourthswitching device controlled by the scan pulse from the (n−p)th stage andconnected between the set node and the second discharging voltage line.

Alternatively, the node controller of the nth stage may further includea fourth switching device controlled by a scan pulse from an (n+q)th oneof the stages (where q is a natural number) and connected between theoutput terminal and the first discharging voltage line.

In accordance with another aspect of the present invention, the nodecontroller of an nth one of the stages (where n is a natural number) mayinclude a first switching device controlled by any one of the clockpulses and connected between the output terminal of an (n−p)th one ofthe stages (where p is a natural number less than n) and a preset node,a second switching device controlled by any one of the clock pulses andconnected between the set node and a second discharging voltage linetransferring a second discharging voltage, a third switching devicecontrolled by a voltage at the preset node and connected between asecond charging voltage line transferring a second charging voltage andthe set node, a fourth switching device controlled by any one of theclock pulses and connected between the second charging voltage line anda reset node, and a fifth switching device controlled by the voltage atthe preset node and connected between the reset node and the seconddischarging voltage line, and the output unit may further include apull-down switching device controlled by a voltage at the reset node andconnected between the output terminal and a first discharging voltageline transferring a first discharging voltage, wherein the firstswitching device, the second switching device and the fourth switchingdevice may all be supplied with the same clock pulse, wherein the clockpulse supplied to the first switching device, second switching deviceand fourth switching device may have a low duration coinciding with ahigh duration of a scan pulse output from the nth stage, wherein theclock pulse supplied to the first switching device, second switchingdevice and fourth switching device may have a high duration partiallyoverlapping with a high duration of a scan pulse from the (n−p)th stage.

In accordance with another aspect of the present invention, the nodecontroller of an nth one of the stages (where n is a natural number) mayinclude a first switching device controlled by any one of the clockpulses and connected between the output terminal of an (n−p)th one ofthe stages (where p is a natural number less than n) and a first presetnode, a second switching device controlled by any one of the clockpulses and connected between a second preset node and a seconddischarging voltage line transferring a second discharging voltage, athird switching device controlled by any one of the clock pulses andconnected between the set node and the second discharging voltage line,a fourth switching device controlled by a voltage at the first presetnode and connected between a third charging voltage line transferring athird charging voltage and the second preset node, and a fifth switchingdevice controlled by a voltage at the second preset node and connectedbetween a second charging voltage line transferring a second chargingvoltage and the set node, wherein the first switching device, the secondswitching device, the third switching device and the pull-down switchingdevice may all be supplied with the same clock pulse, wherein the clockpulse supplied to the first switching device, second switching device,third switching device and pull-down switching device may have a lowduration coinciding with a high duration of a scan pulse output from thenth stage, wherein the clock pulse supplied to the first switchingdevice, second switching device, third switching device and pull-downswitching device may have a high duration partially overlapping with ahigh duration of a scan pulse from the (n−p)th stage.

In accordance with another aspect of the present invention, the nodecontroller of an nth one of the stages (where n is a natural number) mayinclude a first switching device controlled by any one of the clockpulses and connected between the output terminal of an (n−p)th one ofthe stages (where p is a natural number less than n) and a forwardpreset node, a second switching device controlled by any one of theclock pulses and connected between the set node and a second dischargingvoltage line transferring a second discharging voltage, a thirdswitching device controlled by a voltage at the forward preset node andconnected between a forward voltage line transferring a forward voltageand the set node, a fourth switching device controlled by any one of theclock pulses and connected between a reverse preset node and the outputterminal of an (n+q)th stage (where q is a natural number), and a fifthswitching device controlled by a voltage at the reverse preset node andconnected between the set node and a reverse voltage line transferring areverse voltage, wherein the first switching device, the secondswitching device, the fourth switching device and the pull-downswitching device may all be supplied with the same clock pulse, whereinthe clock pulse supplied to the first switching device, second switchingdevice, fourth switching device and pull-down switching device may havea low duration coinciding with a high duration of a scan pulse outputfrom the nth stage, wherein the clock pulse supplied to the firstswitching device, second switching device, fourth switching device andpull-down switching device may have a high duration partiallyoverlapping with a high duration of a scan pulse from the (n−p)th stageor a high duration of a scan pulse from the (n+q)th stage.

In accordance with a further aspect of the present invention, the nodecontroller of an nth one of the stages (where n is a natural number) mayinclude a first switching device controlled by any one of the clockpulses and connected between the output terminal of an (n−p)th one ofthe stages (where p is a natural number less than n) and a forwardpreset node, a second switching device controlled by any one of theclock pulses and connected between a common preset node and a seconddischarging voltage line transferring a second discharging voltage, athird switching device controlled by any one of the clock pulses andconnected between the set node and the second discharging voltage line,a fourth switching device controlled by a voltage at the forward presetnode and connected between a forward voltage line transferring a forwardvoltage and the common preset node, a fifth switching device controlledby a voltage at the common preset node and connected between a secondcharging voltage line transferring a second charging voltage and the setnode, a sixth switching device controlled by any one of the clock pulsesand connected between a reverse preset node and the output terminal ofan (n+q)th stage (where q is a natural number), and a seventh switchingdevice controlled by a voltage at the reverse preset node and connectedbetween the common preset node and a reverse voltage line transferring areverse voltage, wherein the first switching device, the secondswitching device, the third switching device, the sixth switching deviceand the pull-down switching device may all be supplied with the sameclock pulse, wherein the clock pulse supplied to the first switchingdevice, second switching device, third switching device, sixth switchingdevice and pull-down switching device may have a low duration coincidingwith a high duration of a scan pulse output from the nth stage, whereinthe clock pulse supplied to the first switching device, second switchingdevice, third switching device, sixth switching device and pull-downswitching device may have a high duration partially overlapping with ahigh duration of a scan pulse from the (n−p)th stage or a high durationof a scan pulse from the (n+q)th stage.

The forward voltage may be higher than the reverse voltage in forwarddriving, and the reverse voltage may be higher than the forward voltagein reverse driving.

On the other hand, the nth stage may further include a first capacitorconnected between the set node and the output terminal, and a secondcapacitor connected between the first preset node and the second presetnode.

The third charging voltage may be the same as any one of the firstcharging voltage and second charging voltage.

The node controller of the nth stage may further include a sixthswitching device controlled by a scan pulse from an (n+q)th stage (whereq is a natural number) and connected between the output terminal of thenth stage and the first discharging voltage line.

Alternatively, the nth stage may further include a first capacitorconnected between the set node and the output terminal, a secondcapacitor connected between the forward preset node and the set node,and a third capacitor connected between the set node and the reversepreset node.

As another alternative, the nth stage may further include a firstcapacitor connected between the set node and the output terminal, asecond capacitor connected between the forward preset node and thecommon preset node, and a third capacitor connected between the commonpreset node and the reverse preset node.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a block diagram showing the configuration of a shift registeraccording to an embodiment of the present invention;

FIG. 2 is a timing diagram of various signals which are supplied to theshift register of FIG. 1 and various signals which are output therefrom;

FIG. 3 is a circuit diagram of an arbitrary nth stage according to afirst embodiment of the present invention;

FIG. 4 is a circuit diagram of an arbitrary nth stage according to asecond embodiment of the present invention;

FIG. 5 is a circuit diagram of an arbitrary nth stage according to athird embodiment of the present invention;

FIG. 6 is a circuit diagram of an arbitrary nth stage according to afourth embodiment of the present invention;

FIG. 7 is a timing diagram illustrating an output waveform from thestage of FIG. 6;

FIG. 8 is a circuit diagram of an arbitrary nth stage according to afifth embodiment of the present invention;

FIG. 9 is a circuit diagram of an arbitrary nth stage according to asixth embodiment of the present invention;

FIG. 10 is a circuit diagram of an arbitrary nth stage according to aseventh embodiment of the present invention;

FIG. 11 is a timing diagram of clock pulses used in reverse driving;

FIG. 12 is a circuit diagram of an arbitrary nth stage according to aneighth embodiment of the present invention;

FIG. 13 is a simulated waveform diagram illustrating relationships amongvarious signals which are supplied to the shift register of FIG. 1;

FIG. 14 is a simulated waveform diagram illustrating relationships amonga voltage at a preset node, a voltage at a set node and a voltage of ascan pulse in the present invention;

FIG. 15 is a simulated waveform diagram of first to fourth scan pulsesin the present invention; and

FIG. 16 is a simulated waveform diagram of a voltage at a preset node, avoltage at a set node and first to fourth scan pulses in the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a block diagram showing the configuration of a shift registeraccording to an embodiment of the present invention, and FIG. 2 is atiming diagram of various signals which are supplied to the shiftregister of FIG. 1 and various signals which are output therefrom.

The shift register according to the present embodiment includes m stagesST1 to STm, as shown in FIG. 1. Each of the stages ST1 to STm outputsone scan pulse SP1 to SPm for one frame period through an outputterminal OT thereof. At this time, as shown in FIG. 2, the stages ST1 toSTm output the scan pulses SP1 to SPm in such a manner that highdurations of scan pulses output in adjacent periods partially overlapwith each other.

Each of the stages ST1 to STm drives a gate line connected thereto usingthe scan pulse. Also, each of the stages ST1 to STm controls theoperation of a stage downstream therefrom using the scan pulse. Eachstage may control the operations of stages upstream and downstreamtherefrom according to an internal circuit configuration thereof. Inthis case, a dummy stage may further be provided in addition to theabove stages. This dummy stage is connected only to any one of the abovestages, not to a gate line.

The stages ST1 to STm output the scan pulses in order from the firststage ST1 to the mth stage STm. That is, the first stage ST1 outputs thefirst scan pulse SP1, the second stage ST2 then outputs the second scanpulse SP2, the third stage ST3 then outputs the third scan pulse SP3, .. . , and the mth stage STm finally outputs the mth scan pulse SPm.

The scan pulses SP1 to SPm output from the stages ST1 to STm aresequentially supplied to gate lines of a liquid crystal panel (notshown) to sequentially scan the gate lines. Also, the scan pulse outputfrom each of the stages ST1 to STm is supplied only to an upstreamstage, is supplied to the upstream stage and a downstream stage or issupplied only to the downstream stage. For example, a scan pulse outputfrom an nth stage (where n is a natural number less than m) may besupplied to an nth gate line and an (n+q)th stage (where q is a naturalnumber), as shown in FIG. 1. Here, n is a natural number less than m,and the nth stage means any one of the m stages.

This shift register may be built in the liquid crystal panel. That is,the liquid crystal panel has a display region for displaying an image,and a non-display region surrounding the display region, and the shiftregister is built in the non-display region.

Each of the stages ST1 to STm of the shift register, configured in thismanner, is supplied with a first charging voltage VDD1, a secondcharging voltage VDD2, a first discharging voltage VSS1, a seconddischarging voltage VSS2, and any one of first to fourth clock pulsesCLK1 to CLK4 which are output sequentially out of phase with one anotherand cyclically. On the other hand, the first stage ST1 among the stagesST1 to STm is further supplied with a start pulse Vst.

The first and second charging voltages VDD1 and VDD2 are mainly used tocharge nodes of each stage ST1 to STm, and the first and seconddischarging voltages VSS1 and VSS2 are mainly used to discharge thenodes and output terminal OT of each stage ST1 to STm.

The first and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 are all direct current (DC)voltages. The first and second charging voltages VDD1 and VDD2 may bepositive and the first and second discharging voltages VSS1 and VSS2 maybe negative. Here, at least one of the first and second dischargingvoltages VSS1 and VSS2 may be a ground voltage.

The first to fourth clock pulses CLK1 to CLK4 are signals which are usedfor the respective stages ST1 to STm to generate the scan pulses SP1 toSPm. Each stage ST1 to STm receives any one of the first to fourth clockpulses CLK1 to CLK4 and outputs a corresponding one of the scan pulsesSP1 to SPm. For example, a (4n+1)th stage may output a correspondingscan pulse using the first clock pulse CLK1, a (4n+2)th stage may outputa corresponding scan pulse using the second clock pulse CLK2, a (4n+3)thstage may output a corresponding scan pulse using the third clock pulseCLK3, and a (4n+4)th stage may output a corresponding scan pulse usingthe fourth clock pulse CLK4.

The respective high voltages of these clock pulses CLK1 to CLK4 are allthe same and the respective low voltages thereof are all the same.

These clock pulses CLK1 to CLK4 are sequentially output in such a mannerthat low durations thereof partially overlap with each other. Forexample, the first clock pulse CLK1 and second clock pulse CLK2 adjacentto each other may be output in such a manner that low durations thereofoverlap with each other for a time corresponding to about ⅓H (horizontalperiod). Alternatively, the overlap time may be ½H. As the low durationsof the adjacent clock pulses overlap with each other in this manner, thescan pulses have characteristics same as those of the clock pulses, too.That is, the scan pulses are output in such a manner that high durationsof scan pulses output in adjacent periods overlap with each other for acertain period. Accordingly, the high duration of a scan pulse outputfrom any one stage coincides with the low duration of a clock pulsesupplied to that stage.

On the other hand, the start pulse Vst may overlap with the first clockpulse CLK1 or fourth clock pulse CLK4.

Although the four types of clock pulses having different phases are usedfor illustrative purposes in the present invention, any number of typesof clock pulses may be used as long as they are two or more.

Here, the low voltage of any one of the clock pulses CLK1 to CLK4 islower than or equal to the second discharging voltage VSS2, which islower than or equal to the first discharging voltage VSS1.

Also, the high voltage of any one of the clock pulses CLK1 to CLK4 islower than or equal to the first charging voltage VDD1, which is lowerthan or equal to the second charging voltage VDD2.

Each stage ST1 to STm is enabled in response to a scan pulse from anupstream stage. For example, as shown in FIG. 1, the nth stage isenabled in response to a scan pulse from an (n−1)th stage.Exceptionally, the first stage ST1 is enabled in response to the startpulse Vst from a timing controller (not shown).

Each stage ST1 to STm may be disabled by a clock pulse supplied theretoor a scan pulse from a downstream stage. For example, as shown in FIG.1, the second stage ST2 may be disabled by the second clock pulse CLK2.

Hereinafter, a circuit configuration of each stage will be described indetail. All of the stages are the same in configuration, and theconfiguration of the nth stage, which is one arbitrary stage, will thusbe representatively described.

FIG. 3 is a circuit diagram of an arbitrary nth stage according to afirst embodiment of the present invention. The stages according to thisfirst embodiment are supplied with the clock pulses CLK1 to CLK4 asshown in FIG. 2.

Each stage according to the first embodiment of the present inventionincludes, as shown in FIG. 3, a node controller NC for controlling acharging duration of a set node Q, and an output unit OB for outputtinga corresponding scan pulse through an output terminal OT for thecharging duration of the set node Q.

The node controller NC maintains the charging duration for a timecorresponding to a low duration of any one of the plurality of clockpulses CLK1 to CLK4 having phase differences therebetween.

The output unit OB outputs the scan pulse of a high state for thecharging duration by outputting the first charging voltage VDD1 for thecharging duration.

To this end, the output unit OB and the node controller NC haveconfigurations as follows.

The output unit OB of the nth stage includes a pull-up switching deviceTrU and a pull-down switching device TrD.

The pull-up switching device TrU is controlled by a voltage at the setnode Q and is connected between a first charging voltage line whichtransfers the first charging voltage VDD1 and the output terminal OT ofthe nth stage.

The pull-down switching device TrD is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofthe nth stage and a first discharging voltage line which transfers thefirst discharging voltage VSS1. For example, the pull-down switchingdevice TrD of the (4n+1)th stage may be controlled by the first clockpulse CLK1, the pull-down switching device TrD of the (4n+2)th stage maybe controlled by the second clock pulse CLK2, the pull-down switchingdevice TrD of the (4n+3)th stage may be controlled by the third clockpulse CLK3, and the pull-down switching device TrD of the (4n+4)th stagemay be controlled by the fourth clock pulse CLK4.

The node controller NC of the nth stage (where n is a natural number)includes first to third switching devices Tr1 to Tr3.

The first switching device Tr1 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofan (n−p)th stage (where p is a natural number less than n) and a presetnode PN. For example, the first switching device Tr1 of the second stageST2 may be controlled by the second clock pulse CLK2 and be connectedbetween the output terminal OT of the first stage ST1 and the presetnode PN of the second stage ST2.

The second switching device Tr2 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the set node Q and a seconddischarging voltage line which transfers the second discharging voltageVSS2. For example, the second switching device Tr2 of the second stageST2 may be controlled by the second clock pulse CLK2 and be connectedbetween the set node Q and the second discharging voltage line.

The third switching device Tr3 is controlled by a voltage at the presetnode PN and is connected between a second charging voltage line whichtransfers the second charging voltage VDD2 and the set node Q.

Here, the first switching device Tr1, the second switching device Tr2and the pull-down switching device TrD are all supplied with the sameclock pulse.

The low duration of the clock pulse supplied to the first switchingdevice Tr1, second switching device Tr2 and pull-down switching deviceTrD coincides with the high duration of the scan pulse output from thenth stage.

Also, the high duration of the clock pulse supplied to the firstswitching device Tr1, second switching device Tr2 and pull-downswitching device TrD partially overlaps with the high duration of a scanpulse from the (n-p)th stage. For example, the clock pulse supplied tothe first switching device Tr1, second switching device Tr2 andpull-down switching device TrD of the second stage ST2 may be the secondclock pulse CLK2, the high duration of which may partially overlap withthe high duration of the first scan pulse SP1 output from the firststage ST1, as shown in FIG. 2.

The operation of the nth stage configured in this manner willhereinafter be described in detail with reference to FIGS. 2 and 3.Here, it is assumed that the nth stage is the second stage ST2.

First, a description will be given of an operation in a preset periodTp.

The first switching device Tr1 of the second stage ST2 is kept turned onduring the high duration of the second clock pulse CLK2. As shown inFIG. 2, the high duration of the second clock pulse CLK2 and the highduration of the first scan pulse SP1 partially overlap with each other,and the preset node PN is charged for a period in which those highdurations overlap. That is, the first scan pulse SP1 is supplied to thepreset node PN through the first switching device Tr1 turned on by thesecond clock pulse CLK2. Because a high to low transition of the secondclock pulse CLK2 precedes that of the first scan pulse SP1, the firstscan pulse SP1 of a high state is supplied to the preset node PN for aperiod from the turning-on to turning-off of the first switching deviceTr1. As a result, for the preset period Tp, which is the period in whichthe high durations of the second clock pulse CLK2 and first scan pulseSP1 overlap, the preset node PN is charged with a voltage of high logic.Accordingly, the third switching device Tr3, connected to the presetnode PN through the gate electrode thereof, is turned on, and the secondcharging voltage VDD2 is supplied to the set node Q through theturned-on third switching device Tr3.

On the other hand, in this preset period Tp, the second switching deviceTr2 is also turned on by the second clock pulse CLK2 of the high state,and the second discharging voltage VSS2 is supplied to the set node Qthrough the turned-on second switching device Tr2.

In this manner, voltages of opposite logics, the second charging voltageVDD2 corresponding to a voltage of high logic and the second dischargingvoltage VSS2 corresponding to a voltage of low logic are togethersupplied to the preset node PN. At this time, the voltage at the setnode Q is kept discharged by the second discharging voltage VSS2corresponding to the voltage of the low logic, because the area of thesecond switching device Tr2 providing the second discharging voltageVSS2 is set to be larger than that of the third switching device Tr3providing the second charging voltage VDD2. As a result, the pull-upswitching device TrU, connected to the discharged set node Q through thegate electrode thereof, is turned off.

On the other hand, in this preset period Tp, the pull-down switchingdevice TrD is also turned on by the second clock pulse CLK2 of the highstate, and the first discharging voltage VSS1 is supplied to the outputterminal OT through the turned-on pull-down switching device TrD.

Next, a description will be given of an operation in an output periodTo.

In the output period To, the second clock pulse CLK2 makes a high to lowtransition, thereby causing the first switching device Tr1, secondswitching device Tr2 and pull-down switching device TrD, supplied withthe second clock pulse CLK2 through the gate electrodes thereof, to beall turned off.

As the first switching device Tr1 is turned off, the preset node PNfloats, and a voltage corresponding to the first scan pulse SP1 of thehigh state is maintained at the floating preset node PN. Accordingly,the third switching device Tr3, connected to the preset node PN throughthe gate electrode thereof, still remains turned on even in the outputperiod To. At this time, the voltage at the floating preset node PN isbootstrapped by a parasitic capacitor of the third switching device Tr3and the second charging voltage VDD2 applied to the drain electrode ofthe third switching device Tr3, thereby causing the third switchingdevice Tr3 to be completely turned on in the output period To, so as tosupply the second charging voltage VDD2 to the set node Q with littleloss.

Particularly, in this output period To, the second discharging voltageVSS2 is no longer supplied to the set node Q as the second switchingdevice Tr2 is turned off. As a result, in the output period To, the setnode Q is charged with the second charging voltage VDD2. Accordingly,the pull-up switching device TrU, connected to the charged set node Qthrough the gate electrode thereof, is turned on, and the first chargingvoltage VDD1 is output through the turned-on pull-up switching deviceTrU. That is, the pull-up switching device TrU outputs the firstcharging voltage VDD1 as the second scan pulse SP2 and supplies it tothe second gate line and the third stage ST3 through the output terminalOT of the second stage ST2. At this time, the second scan pulse SP2supplied to the third stage ST3 is applied to the drain electrode of thefirst switching device Tr1 of the third stage ST3.

On the other hand, in this output period To, the second clock pulse CLK2of a low state is supplied to the gate electrode of the second switchingdevice Tr2 and the second discharging voltage VSS2 is supplied to thesource electrode of the second switching device Tr2. Particularly, thevoltage of the second clock pulse CLK2 of the low state is set to belower than the second discharging voltage VSS2, thereby making itpossible to prevent leakage current from the second switching deviceTr2. Consequently, in the output period To, leakage of current from theset node Q is prevented, so that the pull-up transistor TrU can normallyoutput the scan pulse.

Next, a description will be given of an operation in a reset periodT_(R).

In the reset period T_(R), the second clock pulse CLK2 returns to thehigh state. As a result, the first switching device Tr1, secondswitching device Tr2 and pull-down switching device TrD, supplied withthe second clock pulse CLK2 through the gate electrodes thereof, are allturned on.

Particularly, in this reset period T_(R), the first scan pulse SP1 iskept low. Accordingly, the first scan pulse SP1 of the low state issupplied to the preset node PN through the turned-on first switchingdevice Tr1. Consequently, the preset node PN is discharged, and thethird switching device Tr3, connected to the discharged preset node PNthrough the gate electrode thereof, is turned off.

On the other hand, the second discharging voltage VSS2 is supplied tothe set node Q through the turned-on second switching device Tr2, so asto discharge the set node Q. As a result, the pull-up switching deviceTrU, connected to the discharged set node Q through the gate electrodethereof, is turned off.

Consequently, in this reset period T_(R), the first discharging voltageVSS1 is supplied to the output terminal OT through the turned-onpull-down switching device TrD.

On the other hand, in this reset period T_(R), the voltage at the presetnode PN, the voltage at the set node Q and the voltage at the outputterminal OT are periodically discharged respectively by the first scanpulse SP1 of the low state, the second discharging voltage VSS2 and thefirst discharging voltage VSS1 based on the periodically supplied secondclock pulse CLK2 of the high state, so that stability of the circuit canbe secured.

Through these preset period Tp, output period To and reset period T_(R),the second stage ST2 outputs the second scan pulse SP2 which is kepthigh for the output period To. In conclusion, the time length of theoutput period To is the same as the previously stated charging duration.

Also, the other stages output their respective scan pulses through thepreset period Tp, output period To and reset period T_(R) in the samemanner.

FIG. 4 is a circuit diagram of an arbitrary nth stage according to asecond embodiment of the present invention. The stages according to thissecond embodiment are supplied with the clock pulses CLK1 to CLK4 asshown in FIG. 2.

Each stage according to the second embodiment of the present inventionfurther includes first and second capacitors C1 and C2 in addition tothe above-stated configuration of the first embodiment, as shown in FIG.4.

The first and second capacitors C1 and C2 are used to more effectivelybootstrap the voltage at the set node Q and the voltage at the presetnode PN, respectively. Also, the first and second capacitors C1 and C2function to reduce a ripple of the voltage at the set node Q and aripple of the voltage at the preset node PN, respectively.

The other components of the second embodiment, not described, are thesame as those of the first embodiment, stated above. For example, thefirst and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 in the second embodiment havethe same characteristics as those in the first embodiment.

FIG. 5 is a circuit diagram of an arbitrary nth stage according to athird embodiment of the present invention. The stages according to thisthird embodiment are supplied with the clock pulses CLK1 to CLK4 asshown in FIG. 2.

Each stage according to the third embodiment of the present inventionfurther includes a fourth switching device Tr4 in addition to theabove-stated configuration of the first embodiment, as shown in FIG. 5.The fourth switching device Tr4 may be provided in any one of the nodecontroller NC and output unit OB. FIG. 5 shows an example in which thefourth switching device Tr4 is provided in the node controller NC.

The fourth switching device Tr4 of the nth stage according to the thirdembodiment is controlled by the scan pulse from the (n−p)th stage and isconnected between the set node Q and the second discharging voltageline. For example, the fourth switching device Tr4 may be controlled bythe scan pulse from the (n−1)th stage.

The further provision of the fourth switching device Tr4 has theadvantage of reducing the area of the second switching device Tr2 drivendirectly by the clock pulse as compared with that in the firstembodiment.

The other components of the third embodiment, not described, are thesame as those of the first embodiment, stated above. For example, thefirst and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 in the third embodiment havethe same characteristics as those in the first embodiment.

FIG. 6 is a circuit diagram of an arbitrary nth stage according to afourth embodiment of the present invention, and FIG. 7 is a timingdiagram illustrating an output waveform from the stage of FIG. 6.

The stages according to this fourth embodiment are supplied with theclock pulses CLK1 to CLK4 as shown in FIG. 2.

Each stage according to the fourth embodiment of the present inventionfurther includes a fourth switching device Tr4 in addition to theabove-stated configuration of the first embodiment, as shown in FIG. 6.The fourth switching device Tr4 may be provided in any one of the nodecontroller NC and output unit OB. FIG. 6 shows an example in which thefourth switching device Tr4 is provided in the node controller NC.

The fourth switching device Tr4 of the nth stage according to the fourthembodiment is controlled by a scan pulse from an (n+q)th stage (where qis a natural number) and is connected between the output terminal OT andthe first discharging voltage line. For example, the fourth switchingdevice Tr4 may be controlled by a scan pulse from an (n+1)th stage or ascan pulse from an (n+2)th stage. FIG. 7 shows an example in which thescan pulse from the (n+1)th stage is supplied to the gate electrode ofthe fourth switching device Tr4.

This fourth switching device Tr4 drops the voltage at the outputterminal of a corresponding stage in response to a scan pulse from adownstream stage. As a result, the scan pulse from each stage slightlyfalls at the time that the scan pulse from the downstream stage makes alow to high transition, as shown in FIG. 7. Consequently, each scanpulse has a low state, a high state, and a middle state. That is, eachscan pulse makes a high to low transition, not directly, but via themiddle state, thereby making it possible to reduce a kickback voltagewithin the liquid crystal panel.

On the other hand, in the case where the scan pulse from the (n+2)thstage is supplied to the gate electrode of the fourth switching deviceTr4 instead of the scan pulse from the (n+1)th stage, each scan pulsedoes not have the above middle state. That is, in this case, each scanpulse has a square wave of a form as shown in FIG. 2.

The other components of the fourth embodiment, not described, are thesame as those of the first embodiment, stated above. For example, thefirst and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 in the fourth embodiment havethe same characteristics as those in the first embodiment.

FIG. 8 is a circuit diagram of an arbitrary nth stage according to afifth embodiment of the present invention. The stages according to thisfifth embodiment are supplied with the clock pulses CLK1 to CLK4 asshown in FIG. 2.

Each stage according to the fifth embodiment of the present inventionincludes, as shown in FIG. 8, a node controller NC for controlling acharging duration of a set node Q, and an output unit OB for outputtinga corresponding scan pulse through an output terminal OT for thecharging duration of the set node Q.

The node controller NC of the nth stage (where n is a natural number)includes first to fifth switching devices Tr1 to Tr5.

The first switching device Tr1 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofan (n−p)th stage (where p is a natural number less than n) and a presetnode PN. For example, the first switching device Tr1 of the second stageST2 may be controlled by the second clock pulse CLK2 and be connectedbetween the output terminal OT of the first stage ST1 and the presetnode PN of the second stage ST2.

The second switching device Tr2 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the set node Q and a seconddischarging voltage line which transfers the second discharging voltageVSS2. For example, the second switching device Tr2 of the second stageST2 may be controlled by the second clock pulse CLK2 and be connectedbetween the set node Q and the second discharging voltage line.

The third switching device Tr3 is controlled by a voltage at the presetnode PN and is connected between a second charging voltage line whichtransfers the second charging voltage VDD2 and the set node Q.

The fourth switching device Tr4 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the second charging voltageline and a reset node QB. For example, the fourth switching device Tr4of the second stage ST2 may be controlled by the second clock pulseCLK2.

The fifth switching device Tr5 is controlled by the voltage at thepreset node PN and is connected between the reset node QB and the seconddischarging voltage line.

The output unit OB of the nth stage includes a pull-up switching deviceTrU and a pull-down switching device TrD.

The pull-up switching device TrU is controlled by a voltage at the setnode Q and is connected between a first charging voltage line whichtransfers the first charging voltage VDD1 and the output terminal OT ofthe nth stage.

The pull-down switching device TrD is controlled by a voltage at thereset node QB and is connected between the output terminal OT of the nthstage and a first discharging voltage line which transfers the firstdischarging voltage VSS1.

Here, the first switching device Tr1, the second switching device Tr2and the fourth switching device Tr4 are all supplied with the same clockpulse.

The low duration of the clock pulse supplied to the first switchingdevice Tr1, second switching device Tr2 and fourth switching device Tr4coincides with the high duration of the scan pulse output from the nthstage.

Also, the high duration of the clock pulse supplied to the firstswitching device Tr1, second switching device Tr2 and fourth switchingdevice Tr4 partially overlaps with the high duration of a scan pulsefrom the (n−p)th stage. For example, the clock pulse supplied to thefirst switching device Tr1, second switching device Tr2 and fourthswitching device Tr4 of the second stage ST2 may be the second clockpulse CLK2, the high duration of which may partially overlap with thehigh duration of the first scan pulse SP1 output from the first stageST1, as shown in FIG. 2.

The pull-down switching device TrD is not driven directly by the clockpulse, but is controlled by the voltage at the reset node QB, so that aload on the clock pulse can be reduced.

Here, the voltage state of the reset node QB is controlled by the fourthand fifth switching devices Tr4 and Tr5. That is, the fourth switchingdevice Tr4 acts to charge the reset node QB with the second chargingvoltage VDD2 in a reset period T_(R), whereas the fifth switching deviceTr5 acts to discharge the reset node QB with the second dischargingvoltage VSS2 in a preset period Tp and an output period To.

The other components of the fifth embodiment, not described, are thesame as those of the first embodiment, stated above. For example, thefirst and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 in the fifth embodiment havethe same characteristics as those in the first embodiment.

FIG. 9 is a circuit diagram of an arbitrary nth stage according to asixth embodiment of the present invention. The stages according to thissixth embodiment are supplied with the clock pulses CLK1 to CLK4 asshown in FIG. 2.

Each stage according to the sixth embodiment of the present inventionincludes, as shown in FIG. 9, a node controller NC for controlling acharging duration of a set node Q, an output unit OB for outputting acorresponding scan pulse through an output terminal OT for the chargingduration of the set node Q, and first and second capacitors C1 and C2.

The first capacitor C1 is connected between the set node Q and theoutput terminal OT, and the second capacitor C2 is connected between afirst preset node PN1 and a second preset node PN2.

The node controller NC of the nth stage (where n is a natural number)includes first to sixth switching devices Tr1 to Tr6.

The first switching device Tr1 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofan (n−p)th stage (where p is a natural number less than n) and the firstpreset node PN1. For example, the first switching device Tr1 of thesecond stage ST2 may be controlled by the second clock pulse CLK2 and beconnected between the output terminal OT of the first stage ST1 and thefirst preset node PN1 of the second stage ST2.

The second switching device Tr2 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the second preset node PN2and a second discharging voltage line which transfers the seconddischarging voltage VSS2. For example, the second switching device Tr2of the second stage ST2 may be controlled by the second clock pulseCLK2.

The third switching device Tr3 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the set node Q and thesecond discharging voltage line. For example, the third switching deviceTr3 of the second stage ST2 may be controlled by the second clock pulseCLK2.

The fourth switching device Tr4 is controlled by a voltage at the firstpreset node PN1 and is connected between a second charging voltage linewhich transfers the second charging voltage VDD2 and the second presetnode PN2. On the other hand, the fourth switching device Tr4 may beconnected to a third charging voltage line (not shown) instead of thesecond charging voltage line. The third charging voltage line transfersa third charging voltage (not shown). The third charging voltage may bethe same as any one of the first charging voltage VDD1 and secondcharging voltage VDD2.

The fifth switching device Tr5 is controlled by a voltage at the secondpreset node PN2 and is connected between the second charging voltageline and the set node Q.

The sixth switching device Tr6 is controlled by a scan pulse from an(n+q)th stage (where q is a natural number) and is connected between theoutput terminal OT of the nth stage and a first discharging voltage linewhich transfers the first discharging voltage VSS1. For example, thesixth switching device Tr6 of the nth stage may be controlled by a scanpulse from an (n+1)th stage and be connected between the output terminalOT of the nth stage and the first discharging voltage line.

The output unit OB of the nth stage includes a pull-up switching deviceTrU and a pull-down switching device TrD.

The pull-up switching device TrU is controlled by a voltage at the setnode Q and is connected between a first charging voltage line whichtransfers the first charging voltage VDD1 and the output terminal OT ofthe nth stage.

The pull-down switching device TrD is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofthe nth stage and the first discharging voltage line which transfers thefirst discharging voltage VSS1. For example, the pull-down switchingdevice TrD of the (4n+1)th stage may be controlled by the first clockpulse CLK1, the pull-down switching device TrD of the (4n+2)th stage maybe controlled by the second clock pulse CLK2, the pull-down switchingdevice TrD of the (4n+3)th stage may be controlled by the third clockpulse CLK3, and the pull-down switching device TrD of the (4n+4)th stagemay be controlled by the fourth clock pulse CLK4.

The other components of the sixth embodiment, not described, are thesame as those of the first embodiment, stated above. For example, thefirst and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 in the sixth embodiment havethe same characteristics as those in the first embodiment.

The operation of the nth stage configured in this manner willhereinafter be described in detail with reference to FIGS. 2 and 9.Here, it is assumed that the nth stage is the second stage ST2.

First, a description will be given of an operation in a preset periodTp.

The first switching device Tr1 of the second stage ST2 is kept turned onduring the high duration of the second clock pulse CLK2. As shown inFIG. 2, the high duration of the second clock pulse CLK2 and the highduration of the first scan pulse SP1 partially overlap with each other,and the first preset node PN1 is charged for a period in which thosehigh durations overlap. That is, the first scan pulse SP1 is supplied tothe first preset node PN1 through the first switching device Tr1 turnedon by the second clock pulse CLK2. Because a high to low transition ofthe second clock pulse CLK2 precedes that of the first scan pulse SP1,the first scan pulse SP1 of a high state is supplied to the first presetnode PN1 for a period from the turning-on to turning-off of the firstswitching device Tr1. As a result, for the preset period Tp, which isthe period in which the high durations of the second clock pulse CLK2and first scan pulse SP1 overlap, the first preset node PN1 is chargedwith a voltage of high logic. Accordingly, the fourth switching deviceTr4, connected to the first preset node PN1 through the gate electrodethereof, is turned on, and the second charging voltage VDD2 is suppliedto the second preset node PN2 through the turned-on fourth switchingdevice Tr4.

On the other hand, in this preset period Tp, the second and thirdswitching devices Tr2 and Tr3 are also turned on by the second clockpulse CLK2 of the high state, and the second discharging voltage VSS2 issupplied to the second preset node PN2 through the turned-on secondswitching device Tr2 and to the set node Q through the turned-on thirdswitching device Tr3.

In this manner, voltages of opposite logics, the second charging voltageVDD2 corresponding to a voltage of high logic and the second dischargingvoltage VSS2 corresponding to a voltage of low logic are togethersupplied to the second preset node PN2. At this time, the voltage at thesecond preset node PN2 is kept discharged by the second dischargingvoltage VSS2 corresponding to the voltage of the low logic, because thearea of the second switching device Tr2 providing the second dischargingvoltage VSS2 is set to be larger than that of the fourth switchingdevice Tr4 providing the second charging voltage VDD2. As a result, thefifth switching device TrU, connected to the discharged second presetnode PN2 through the gate electrode thereof, is turned off.

On the other hand, the set node Q is discharged by the seconddischarging voltage VSS2 supplied thereto by the turned-on thirdswitching device Tr3, and the pull-up switching device TrU, connected tothe discharged set node Q through the gate electrode thereof, is turnedoff.

On the other hand, in this preset period Tp, the pull-down switchingdevice TrD is also turned on by the second clock pulse CLK2 of the highstate, and the first discharging voltage VSS1 is supplied to the outputterminal OT through the turned-on pull-down switching device TrD.

On the other hand, in this preset period Tp, the third scan pulse SP3from the third stage ST3 is low, thereby causing the sixth switchingdevice Tr6, supplied with the third scan pulse SP3 of the low statethrough the gate electrode thereof, to be turned off.

Next, a description will be given of an operation in an output periodTo.

In the output period To, the second clock pulse CLK2 makes a high to lowtransition, thereby causing the first switching device Tr1, secondswitching device Tr2, third switching device Tr3 and pull-down switchingdevice TrD, supplied with the second clock pulse CLK2 through the gateelectrodes thereof, to be all turned off.

As the first switching device Tr1 is turned off, the first preset nodePN1 floats, and a voltage corresponding to the first scan pulse SP1 ofthe high state is maintained at the floating first preset node PN1.Accordingly, the fourth switching device Tr4, connected to the firstpreset node PN1 through the gate electrode thereof, still remains turnedon even in the output period To. At this time, the voltage at thefloating first preset node PN1 is bootstrapped by a parasitic capacitorof the fourth switching device Tr4 and the second charging voltage VDD2applied to the drain electrode of the fourth switching device Tr4,thereby causing the fourth switching device Tr4 to be completely turnedon in the output period To, so as to supply the second charging voltageVDD2 to the second preset node PN2 with little loss.

Particularly, in this output period To, the second discharging voltageVSS2 is no longer supplied to the second preset node PN2 as the secondswitching device Tr2 is turned off. As a result, in the output periodTo, the second preset node PN2 is charged with the second chargingvoltage VDD2. Accordingly, the fifth switching device Tr5, connected tothe charged second preset node PN2 through the gate electrode thereof,is turned on, and the second charging voltage VDD2 is supplied to theset node Q through the turned-on fifth switching device Tr5. Then, theset node Q is charged with the second charging voltage VDD2, and thepull-up switching device TrU, connected to the charged set node Qthrough the gate electrode thereof, is turned on. Consequently, thefirst charging voltage VDD1 is output through the turned-on pull-upswitching device TrU. That is, the pull-up switching device TrU outputsthe first charging voltage VDD1 as the second scan pulse SP2 andsupplies it to the second gate line and the third stage ST3 through theoutput terminal OT of the second stage ST2. At this time, the secondscan pulse SP2 supplied to the third stage ST3 is applied to the drainelectrode of the first switching device Tr1 of the third stage ST3.

On the other hand, in this output period To, the second clock pulse CLK2of the low state is supplied to each of the gate electrodes of thesecond and third switching devices Tr2 and Tr3 and the seconddischarging voltage VSS2 is supplied to each of the source electrodes ofthe second and third switching devices Tr2 and Tr3. Particularly, thevoltage of the second clock pulse CLK2 of the low state is set to belower than the second discharging voltage VSS2, thereby making itpossible to prevent leakage current from the second and third switchingdevices Tr2 and Tr3. Consequently, in the output period To, leakage ofcurrent from the second preset node PN2 and set node Q is prevented, sothat the pull-up transistor TrU can normally output the scan pulse.

Next, a description will be given of an operation in a reset periodT_(R).

In the reset period T_(R), the second clock pulse CLK2 returns to thehigh state. As a result, the first switching device Tr1, secondswitching device Tr2, third switching device Tr3 and pull-down switchingdevice TrD, supplied with the second clock pulse CLK2 through the gateelectrodes thereof, are all turned on.

Particularly, in this reset period T_(R), the first scan pulse SP1 iskept low. Accordingly, the first scan pulse SP1 of the low state issupplied to the first preset node PN1 through the turned-on firstswitching device Tr1. Consequently, the first preset node PN1 isdischarged, and the fourth switching device Tr4, connected to thedischarged first preset node PN1 through the gate electrode thereof, isturned off.

On the other hand, the second discharging voltage VSS2 is supplied tothe second preset node PN2 through the turned-on second switching deviceTr2, so as to discharge the second preset node PN2. As a result, thefifth switching device Tr5, connected to the discharged second presetnode PN2 through the gate electrode thereof, is turned off.

Also, the second discharging voltage VSS2 is supplied to the set node Qthrough the turned-on third switching device Tr3, so as to discharge theset node Q. As a result, the pull-up switching device TrU, connected tothe discharged set node Q through the gate electrode thereof, is turnedoff.

Consequently, in this reset period T_(R), the first discharging voltageVSS1 is supplied to the output terminal OT through the turned-onpull-down switching device TrD.

On the other hand, in an intermediate period between the output periodTo and the reset period T_(R), the sixth switching device Tr6 of thesecond stage ST2 supplies the first discharging voltage VSS1 to theoutput terminal OT of the second stage ST2 in response to the third scanpulse SP3 from the third stage ST3. As a result, the output terminal OTof the second stage ST2 is maintained at a voltage of a middle state inthe intermediate period and, thereafter, at the first dischargingvoltage VSS1 in the reset period T_(R).

On the other hand, in this reset period T_(R), the voltage at the firstpreset node PN1, the voltage at the second preset node PN2, the voltageat the set node Q and the voltage at the output terminal OT areperiodically discharged respectively by the first scan pulse SP1 of thelow state, the second discharging voltage VSS2, the second dischargingvoltage VSS2 and the first discharging voltage VSS1 based on theperiodically supplied second clock pulse CLK2 of the high state, so thatstability of the circuit can be secured.

The other components of the sixth embodiment, not described, are thesame as those of the first embodiment, stated above. For example, thefirst and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 in the sixth embodiment havethe same characteristics as those in the first embodiment.

FIG. 10 is a circuit diagram of an arbitrary nth stage according to aseventh embodiment of the present invention, and FIG. 11 is a timingdiagram of clock pulses used in reverse driving.

In forward driving, the stages according to this seventh embodiment aresupplied with the clock pulses CLK1 to CLK4 as shown in FIG. 2 (referredto hereinafter as forward clock pulses). In contrast, in reversedriving, the stages according to this seventh embodiment are suppliedwith the clock pulses CLK1 to CLK4 as shown in FIG. 11 (referred tohereinafter as reverse clock pulses).

The shift register including the stages according to the seventhembodiment of the present invention may output scan pulses forward andreversely. That is, in the forward driving, the m stages ST1 to STm ofthe shift register output the scan pulses SP1 to SPm sequentially fromthe first stage ST1 to the last stage STm. In contrast, in the reversedriving, the m stages ST1 to STm of the shift register output the scanpulses SP1 to SPm sequentially from the last stage STm to the firststage ST1.

Each stage according to the seventh embodiment of the present inventionincludes, as shown in FIG. 10, a node controller NC for controlling acharging duration of a set node Q, an output unit OB for outputting acorresponding scan pulse through an output terminal OT for the chargingduration of the set node Q, and first to third capacitors C1 to C3.

The first capacitor C1 is connected between the set node Q and theoutput terminal OT, the second capacitor C2 is connected between aforward preset node PN_F and the set node Q, and the third capacitor C3is connected between the set node Q and a reverse preset node PN_R.

The node controller NC maintains the charging duration for a timecorresponding to a low duration of any one of the plurality of clockpulses CLK1 to CLK4 having phase differences therebetween.

The output unit OB outputs the scan pulse of a high state for thecharging duration by outputting the first charging voltage VDD1 for thecharging duration.

To this end, the output unit OB and the node controller NC haveconfigurations as follows.

The output unit OB of the nth stage includes a pull-up switching deviceTrU and a pull-down switching device TrD.

The pull-up switching device TrU is controlled by a voltage at the setnode Q and is connected between a first charging voltage line whichtransfers the first charging voltage VDD1 and the output terminal OT ofthe nth stage.

The pull-down switching device TrD is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofthe nth stage and a first discharging voltage line which transfers thefirst discharging voltage VSS1. For example, the pull-down switchingdevice TrD of the (4n+1)th stage may be controlled by the first clockpulse CLK1, the pull-down switching device TrD of the (4n+2)th stage maybe controlled by the second clock pulse CLK2, the pull-down switchingdevice TrD of the (4n+3)th stage may be controlled by the third clockpulse CLK3, and the pull-down switching device TrD of the (4n+4)th stagemay be controlled by the fourth clock pulse CLK4.

The node controller NC of the nth stage (where n is a natural number)includes first to fifth switching devices Tr1 to Tr5.

The first switching device Tr1 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofan (n−p)th stage (where p is a natural number less than n) and theforward preset node PN_F. For example, the first switching device Tr1 ofthe second stage ST2 may be controlled by the second clock pulse CLK2and be connected between the output terminal OT of the first stage ST1and the forward preset node PN_F of the second stage ST2.

The second switching device Tr2 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the set node Q and a seconddischarging voltage line which transfers the second discharging voltageVSS2. For example, the second switching device Tr2 of the second stageST2 may be controlled by the second clock pulse CLK2 and be connectedbetween the set node Q and the second discharging voltage line.

The third switching device Tr3 is controlled by a voltage at the forwardpreset node PN_F and is connected between a forward voltage line whichtransfers a forward voltage V_F and the set node Q. Here, the forwardvoltage V_F is kept high in the forward driving, whereas low in thereverse driving. The high voltage of the forward voltage V_F may be thesame as the above first charging voltage VDD1 or second charging voltageVDD2. Also, the low voltage of the forward voltage V_F may be the sameas the above first discharging voltage VSS1 or second dischargingvoltage VSS2.

The fourth switching device Tr4 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofan (n+q)th stage (where q is a natural number) and the reverse presetnode PN_R. For example, the fourth switching device Tr4 of the secondstage ST2 may be controlled by the second clock pulse CLK2 and beconnected between the output terminal OT of the third stage ST1 and thereverse preset node PN_R of the second stage ST2.

The fifth switching device Tr5 is controlled by a voltage at the reversepreset node PN_R and is connected between a reverse voltage line whichtransfers a reverse voltage V_R and the set node Q. Here, the reversevoltage V_R is kept high in the reverse driving, whereas low in theforward driving. The high voltage of the reverse voltage V_R may be thesame as the above first charging voltage VDD1 or second charging voltageVDD2. Also, the low voltage of the reverse voltage V_R may be the sameas the above first discharging voltage VSS1 or second dischargingvoltage VSS2.

Here, the first switching device Tr1, the second switching device Tr2,the fourth switching device Tr4 and the pull-down switching device TrDare all supplied with the same clock pulse.

The low duration of the clock pulse supplied to the first switchingdevice Tr1, second switching device Tr2, fourth switching device Tr4 andpull-down switching device TrD coincides with the high duration of thescan pulse output from the nth stage.

In the forward driving, the high duration of the clock pulse (forwardclock pulse) supplied to the first switching device Tr1, secondswitching device Tr2, fourth switching device Tr4 and pull-downswitching device TrD partially overlaps with the high duration of a scanpulse from the (n−p)th stage. For example, the clock pulse supplied tothe first switching device Tr1, second switching device Tr2, fourthswitching device Tr4 and pull-down switching device TrD of the secondstage ST2 may be the second clock pulse CLK2 (second forward clockpulse), the high duration of which may partially overlap with the highduration of the first scan pulse SP1 output from the first stage ST1, asshown in FIG. 2.

Also, in the reverse driving, the high duration of the clock pulse(reverse clock pulse) supplied to the first switching device Tr1, secondswitching device Tr2, fourth switching device Tr4 and pull-downswitching device TrD partially overlaps with the high duration of a scanpulse from the (n+q)th stage.

On the other hand, the forward voltage V_F and reverse voltage V_Rsupplied to the shift register including these stages may haverelationships as follows.

For example, in the forward driving, the forward voltage V_F may behigher than or equal to the first charging voltage VDD1. In this case,the reverse voltage V_R may be the same as the second dischargingvoltage VSS2.

In contrast, in the reverse driving, the reverse voltage V_R may behigher than or equal to the first charging voltage VDD1. In this case,the forward voltage V_F may be the same as the second dischargingvoltage VSS2.

In the forward driving, any one of the forward clock pulses CLK1 to CLK4as shown in FIG. 2 is supplied to the first switching device Tr1, secondswitching device Tr2, fourth switching device Tr4 and pull-downswitching device TrD. In contrast, in the reverse driving, any one ofthe reverse clock pulses CLK1 to CLK4 as shown in FIG. 11 is supplied tothe first switching device Tr1, second switching device Tr2, fourthswitching device Tr4 and pull-down switching device TrD.

The reverse clock pulses CLK1 to CLK4 are output in such a manner thatthe fourth clock pulse CLK4 is output first and the third clock pulseCLK3, second clock pulse CLK2 and first clock pulse CLK1 are then outputin order, as shown in FIG. 11.

The other components of the seventh embodiment, not described, are thesame as those of the first embodiment, stated above. For example, thefirst and second charging voltages VDD1 and VDD2 and the first andsecond discharging voltages VSS1 and VSS2 in the seventh embodiment havethe same characteristics as those in the first embodiment.

FIG. 12 is a circuit diagram of an arbitrary nth stage according to aneighth embodiment of the present invention. In forward driving, thestages according to this eighth embodiment are supplied with the forwardclock pulses CLK1 to CLK4 as shown in FIG. 2. In contrast, in reversedriving, the stages according to this eighth embodiment are suppliedwith the reverse clock pulses CLK1 to CLK4 as shown in FIG. 11.

The shift register including the stages according to the eighthembodiment of the present invention may output scan pulses forward andreversely in the same manner as in the above seventh embodiment.

Each stage according to the eighth embodiment of the present inventionincludes, as shown in FIG. 12, a node controller NC for controlling acharging duration of a set node Q, an output unit OB for outputting acorresponding scan pulse through an output terminal OT for the chargingduration of the set node Q, and first to third capacitors C1 to C3.

The first capacitor C1 is connected between the set node Q and theoutput terminal OT, the second capacitor C2 is connected between aforward preset node PN_F and a common preset node PN_C, and the thirdcapacitor C3 is connected between the common preset node PN_C and areverse preset node PN_R.

The node controller NC maintains the charging duration for a timecorresponding to a low duration of any one of the plurality of clockpulses CLK1 to CLK4 having phase differences therebetween.

The output unit OB outputs the scan pulse of a high state for thecharging duration by outputting the first charging voltage VDD1 for thecharging duration.

To this end, the output unit OB and the node controller NC haveconfigurations as follows.

The output unit OB of the nth stage includes a pull-up switching deviceTrU and a pull-down switching device TrD.

The pull-up switching device TrU is controlled by a voltage at the setnode Q and is connected between a first charging voltage line whichtransfers the first charging voltage VDD1 and the output terminal OT ofthe nth stage.

The pull-down switching device TrD is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofthe nth stage and a first discharging voltage line which transfers thefirst discharging voltage VSS1. For example, the pull-down switchingdevice TrD of the (4n+1)th stage may be controlled by the first clockpulse CLK1, the pull-down switching device TrD of the (4n+2)th stage maybe controlled by the second clock pulse CLK2, the pull-down switchingdevice TrD of the (4n+3)th stage may be controlled by the third clockpulse CLK3, and the pull-down switching device TrD of the (4n+4)th stagemay be controlled by the fourth clock pulse CLK4.

The node controller NC of the nth stage (where n is a natural number)includes first to seventh switching devices Tr1 to Tr7.

The first switching device Tr1 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofan (n−p)th stage (where p is a natural number less than n) and theforward preset node PN_F. For example, the first switching device Tr1 ofthe second stage ST2 may be controlled by the second clock pulse CLK2and be connected between the output terminal OT of the first stage ST1and the forward preset node PN_F of the second stage ST2.

The second switching device Tr2 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the common preset node PN_Cand a second discharging voltage line which transfers the seconddischarging voltage VSS2. For example, the second switching device Tr2of the second stage ST2 may be controlled by the second clock pulseCLK2.

The third switching device Tr3 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the set node Q and thesecond discharging voltage line. For example, the third switching deviceTr3 of the second stage ST2 may be controlled by the second clock pulseCLK2.

The fourth switching device Tr4 is controlled by a voltage at theforward preset node PN_F and is connected between a forward voltage linewhich transfers a forward voltage V_F and the common preset node PN_C.Here, the forward voltage V_F is kept high in the forward driving,whereas low in the reverse driving. The high voltage of the forwardvoltage V_F may be the same as the above first charging voltage VDD1 orsecond charging voltage VDD2. Also, the low voltage of the forwardvoltage V_F may be the same as the above first discharging voltage VSS1or second discharging voltage VSS2.

The fifth switching device Tr5 is controlled by a voltage at the commonpreset node PN_C and is connected between a second charging voltage linewhich transfers the second charging voltage VDD2 and the set node Q.

The sixth switching device Tr6 is controlled by any one of the clockpulses CLK1 to CLK4 and is connected between the output terminal OT ofan (n+q)th stage (where q is a natural number) and the reverse presetnode PN_R. For example, the sixth switching device Tr6 of the secondstage ST2 may be controlled by the second clock pulse CLK2 and beconnected between the output terminal OT of the third stage ST1 and thereverse preset node PN_R of the second stage ST2.

The seventh switching device Tr7 is controlled by a voltage at thereverse preset node PN_R and is connected between a reverse voltage linewhich transfers a reverse voltage V_R and the common preset node PN_C.Here, the reverse voltage V_R is kept high in the reverse driving,whereas low in the forward driving. The high voltage of the reversevoltage V_R may be the same as the above first charging voltage VDD1 orsecond charging voltage VDD2. Also, the low voltage of the reversevoltage V_R may be the same as the above first discharging voltage VSS1or second discharging voltage VSS2.

Here, the first switching device Tr1, the second switching device Tr2,the third switching device Tr3, the sixth switching device Tr6 and thepull-down switching device TrD are all supplied with the same clockpulse.

The low duration of the clock pulse supplied to the first switchingdevice Tr1, second switching device Tr2, third switching device Tr3,sixth switching device Tr6 and pull-down switching device TrD coincideswith the high duration of the scan pulse output from the nth stage.

In the forward driving, the high duration of the clock pulse (forwardclock pulse) supplied to the first switching device Tr1, secondswitching device Tr2, third switching device Tr3, sixth switching deviceTr6 and pull-down switching device TrD partially overlaps with the highduration of a scan pulse from the (n−p)th stage. For example, the clockpulse supplied to the first switching device Tr1, second switchingdevice Tr2, third switching device Tr3, sixth switching device Tr6 andpull-down switching device TrD of the second stage ST2 may be the secondclock pulse CLK2 (second forward clock pulse), the high duration ofwhich may partially overlap with the high duration of the first scanpulse SP1 output from the first stage ST1, as shown in FIG. 2.

Also, in the reverse driving, the high duration of the clock pulse(reverse clock pulse) supplied to the first switching device Tr1, secondswitching device Tr2, third switching device Tr3, sixth switching deviceTr6 and pull-down switching device TrD partially overlaps with the highduration of a scan pulse from the (n+q)th stage.

On the other hand, the forward voltage V_F and reverse voltage V_Rsupplied to the shift register including these stages may haverelationships as follows.

For example, in the forward driving, the forward voltage V_F may behigher than or equal to the first charging voltage VDD1. In this case,the reverse voltage V_R may be the same as the second dischargingvoltage VSS2.

In contrast, in the reverse driving, the reverse voltage V_R may behigher than or equal to the first charging voltage VDD1. In this case,the forward voltage V_F may be the same as the second dischargingvoltage VSS2.

FIG. 13 is a simulated waveform diagram illustrating relationships amongvarious signals which are supplied to the shift register of FIG. 1.

According to FIG. 13, the second charging voltage VDD2 is highest, thefirst charging voltage VDD1 is next high, the high voltage Vgh of theclock pulse is next high, the first discharging voltage VSS1 is nexthigh and the second discharging voltage VSS2 is lowest. Here, the lowvoltage Vg1 of the clock pulse is the same as the second dischargingvoltage VSS2.

FIG. 14 is a simulated waveform diagram illustrating relationships amonga voltage at a preset node, a voltage at a set node and a voltage of ascan pulse in the present invention.

When the threshold voltage Vth of the second switching device Tr2 in thefirst embodiment is 2V, the voltage at the preset node PN, the voltageat the set node Q and the voltage of the scan pulse SP are set as shownin FIG. 14.

FIG. 15 is a simulated waveform diagram of first to fourth scan pulsesin the present invention.

As can be seen from FIG. 15, the first to fourth scan pulses aresequentially output while overlapping.

FIG. 16 is a simulated waveform diagram of a voltage at a preset node, avoltage at a set node and first to fourth scan pulses in the presentinvention.

When the threshold voltage Vth of the second switching device Tr2 in thefirst embodiment is −3V, the voltage at the preset node PN, the voltageat the set node Q and the voltage of the scan pulse SP are set as shownin FIG. 16.

On the other hand, in all of the embodiments, when voltages to becompared with each other have the same polarity, the comparison is madebased on, not the absolute values of the levels of the voltages, but thelevels themselves. For example, the low voltage of the clock pulse CLKnand the second discharging voltage VSS2 in FIG. 3 may both be negative.In this case, that the low voltage of the clock pulse CLKn is lower thanthe second discharging voltage VSS2 means that the second dischargingvoltage VSS2 is, for example, −5V if the low voltage of the clock pulseCLKn is, for example, −10V.

As is apparent from the above description, a shift register according tothe present invention has effects as follows.

Firstly, a scan pulse is generated using a DC voltage to remove acoupling phenomenon, thereby stabilizing the output of the shiftregister.

Secondly, a DC voltage is used instead of a clock pulse, therebyreducing power consumption compared with conventional cases.

Thirdly, the levels of discharging voltages supplied to the gateelectrode and source electrode of a switching device which is in chargeof discharging of a set node are set in such a manner that thedischarging voltage supplied to the gate electrode is kept lower thanthe discharging voltage supplied to the source electrode, therebycompletely turning off the switching device in an output period, so asto normally generate a scan pulse.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A shift register comprising a plurality of stagesfor sequentially outputting scan pulses in such a manner that highdurations of the scan pulses partially overlap with each other, whereineach of the stages comprises: a node controller for controlling acharging duration of a set node; and an output unit for outputting acorresponding one of the scan pulses through an output terminal for thecharging duration of the set node, wherein the node controller maintainsthe charging duration for a time corresponding to a low duration of anyone of a plurality of clock pulses having phase differencestherebetween, and the output unit outputs the corresponding scan pulseof a high state for the charging duration by selectively outputting afirst charging voltage for the charging duration, the first chargingvoltage being a direct current (DC) voltage, wherein the plurality ofclock pulses are sequentially output in such a manner that low durationsthereof partially overlap with each other, wherein the output unitcomprises a pull-up switching device controlled by a voltage at the setnode and connected between a first charging voltage line transferringthe first charging voltage and the output terminal, wherein the outputunit further comprises a pull-down switching device controlled by anyone of the clock pulses and connected between the output terminal and afirst discharging voltage line transferring a first discharging voltage,and wherein the node controller of an nth one of the stages (where n isa natural number) comprises: a first switching device controlled by anyone of the clock pulses and connected between the output terminal of an(n−p)th one of the stages (where p is a natural number less than n) anda forward preset node; a second switching device controlled by any oneof the clock pulses and connected between a common preset node and asecond discharging voltage line transferring a second dischargingvoltage; a third switching device controlled by any one of the clockpulses and connected between the set node and the second dischargingvoltage line; a fourth switching device controlled by a voltage at theforward preset node and connected between a forward voltage linetransferring a forward voltage and the common preset node; a fifthswitching device controlled by a voltage at the common preset node andconnected between a second charging voltage line transferring a secondcharging voltage and the set node; a sixth switching device controlledby any one of the clock pulses and connected between a reverse presetnode and the output terminal of an (n+q)th stage (where q is a naturalnumber); and a seventh switching device controlled by a voltage at thereverse preset node and connected between the common preset node and areverse voltage line transferring a reverse voltage, wherein the firstswitching device, the second switching device, the third switchingdevice, the sixth switching device and the pull-down switching deviceare all supplied with the same clock pulse, wherein the clock pulsesupplied to the first switching device, the second switching device, thethird switching device, the sixth switching device and the pull-downswitching device has a low duration coinciding with a high duration of ascan pulse output from the nth stage, and wherein the clock pulsesupplied to the first switching device, the second switching device, thethird switching device, the sixth switching device and the pull-downswitching device has a high duration partially overlapping with a highduration of a scan pulse from the (n−p)th stage or a high duration of ascan pulse from the (n+q)th stage.
 2. The shift register according toclaim 1, wherein: the forward voltage is higher than the reverse voltagein forward driving; and the reverse voltage is higher than the forwardvoltage in reverse driving.
 3. The shift register according to claim 1,wherein the nth stage further comprises: a first capacitor connectedbetween the set node and the output terminal; a second capacitorconnected between the forward preset node and the common preset node;and a third capacitor connected between the common preset node and thereverse preset node.